BILLINGS, Mont. — Newly released recordings of 911 calls from hikers who came upon a fatal bear mauling in Yellowstone National Park reveal a harrowing scene in which they heard a bear's roar and a couple screaming before the man went silent and the woman continued to yell for help.

Authorities released the recordings Tuesday along with a report from investigators that concluded the couple's screaming and running possibly triggered the mauling of 57-year-old Brian Matayoshi in early July.

"It sounded like they were trying to scare the bear," an unidentified male hiker told the 911 dispatcher. "I heard a man's voice making loud, like, um, like animal noises. It sounded like he was trying to scare the bear and I heard a woman screaming. It sounded like she was scared."

A short time later, another caller who identified himself as a trauma surgeon called and said he was just a few hundred yards from the scene.

"Did you hear what they were saying? Did they say they were attacked or just yelling for help?" the dispatcher asked.

"No. They were just yelling for help. And all I can here is the lady's voice now. There was a man as well, so I'm worried that the man may be injured," the caller said.

In the immediate aftermath of the attack, park officials said the Matayoshis responded correctly when they encountered the bear along the park's popular Wapiti Lake Trailhead. But following a two-month investigation, bear researchers and wildlife agents concluded the couple's harried, 173-yard retreat after they encountered the bear may have played a role.

"What possibly began as an attempt by the bear to assess the Matayoshis' activities became a sustained pursuit of them as they fled running and yelling on the trail," the investigation team report said.

The couple was not carrying bear spray, mace-like canisters of pressurized pepper spray that park officials advise hikers to carry for self-defense.

The attack took place about 1½ miles from the park's popular Wapiti Lake picnic ground, where the Matayoshis had set out for a hike at about 8:30 a.m. after arriving in the park a day earlier, according to the investigators' report.

The couple first spied the mother grizzly with her two cubs just after 10 a.m., from a vantage point along the trail. It was the Matayoshis fourth visit to the park, but the first in which they had seen any bears.

Danger lurks
As the bears were digging and grazing in an open meadow, the couple stopped and took pictures from a distance of several hundred yards, then hiked on after deciding the animals were not near the trail.

After another half mile, then turned back because they were annoyed by mosquitoes, and soon after saw a large bear off the trail about 100 yards away. They turned and started heading for a patch of nearby trees when Marylyn Matayoshi "saw the bear's head pop up."

"She started coming at us and Brian said 'Run.' We were running down the trail," Marylyn Matayoshi told investigators. She heard her husband yell and turned to see the sow "hit him," with the cubs trailing behind their mother and growling.

After killing the husband, the bear tugged at Marylyn Matayoshi's backpack, then released her and fled. "She walked over to her husband and attempted to use a tourniquet on Brian's leg and heard a long breath escape from Brian," the report said.

She tried to call 911 for help — her cellphone log showed she tried 21 times — but never got through. She started back down the trail several times, but kept turning back out of fear that she would encounter the bears again.

Eventually she walked to the edge of the meadow where the bear charged from and was found by rangers who had been alerted to the attack by other hikers.

Park authorities later decided to let the bear remain free because it had no prior run-ins with humans and was reacting as might be expected to a surprise encounter.

Video: Man dies after grizzly bear attack

Closed captioning of: Man dies after grizzly bear attack

>>>rangers at
yellowstone national park
are trying to trap a
grizzly bear
who killed a camper there last week. nbc's miguel almaguer is in the park with us.

>>good morning. because there are no witnesses to the attack
park rangers
are still trying to piece together a
time line
of what exactly happened, but they say there is no doubt this deadly attack was caused by a grizzly. its beauty is breathtaking, but once again this year,
yellowstone national park
has been deadly. today the mary
mountain trail
is closed. this is where hikers found 59-year-old
john wallace
's body five miles from the trail's
east end
. the avenue individual outdoorsman, husband from michigan, was mauled to death, say
park rangers
, by a grizzly. the second fatal
bear attack
in
yellowstone
this year.

>>he just was a wonderful hunter, kayaking, canoeing, loved the outdoors. he was physically fit.

>> reporter: wallace was alone as he walked the 21-mile trail. grizzly tracks were discovered in the area. and although
park rangers
say food, a
candy bar
, was found on wallace there's no clear cause for the attack.

>>it is a wild place, and we do have predators in
yellowstone
.

>> reporter: with some 3.5 million yearly visitors to
yellowstone
this is the second fate tar
bear attack
in just two months. in july a california man was mauled to death on a popular trail. an estimated 200 grizzlies roam free at
yellowstone
before this deadly summer the last fatality was 25 years ago. and though today rangers are trying to track down a killer bear, they say the park is safe.
park rangers
say there's no reason to suspect that either of the two attacked here are connected. they have laid three traps throughout the park to try to catch the grizzly responsible for last week's